Studies on several regulatory processes controlled by T4 will continue; process S1 (first shutoff) causes the shutoff of synthesis of most T4 early proteins at around 12 min at 37 degrees, while process S2 does the same at 20 min under conditions where S1 fails. We have shown that the T4 regA gene controls S2 for many early proteins, and is probably acting at translation. We are examining ribosomes labeled with radioactive amino acids at various times before and/or after infection, to ask what differences between wild-type T4 and various T4 mutants (including regA) can be detected by one-and two-dimensional electrophoresis. We have found what appears to be the regA protein (molecular weight around 12,000) and will shortly begin purifying it and testing for its presence on ribosomes. We find that when two different amber mutants in the same early T4 gene infect the same cell, very few cells produce phage if the regA gene is wild. However, if the regA function is missing, a high proportion of such cells do produce phage. We would like to interpret this to mean that the regA gene prevents expression of the wild-type, interparental recombinant DNA; but an alternate explanation might be that much more recombinant DNA is made in the regA-defective infection. We will test this in two ways: (a) recombinant DNA will be measured as hybrid-density material in CsC1 gradients after infection by a mixture of density-labeled and unlabeled phage; (b) DNA recombinant in the very gene containing the amber mutations will be measured by transformation. Gorini's lab showed that certain streptomycin-resistant mutants of E. coli develop marked ribosomal ambiguity when grown for many generations in the drug; the effect remains after complete removal of streptomycin. Such cells phenotypically suppress many T4 amber mutants very efficiently. We have found that such suppression is reduced 4-fold (measured as phage production) when the infection is also regA-defective. This suggests a possible interaction of the regA protein with the ribosome. We plan to measure directly the amounts of suppressed amber gene protein by electrophoresis of labeled cell extracts.